Circuit for electric discharge devices



Oct. 215 1947. LEMMERS 2,429,415

CIRCUIT FOR ELECTRIC DISCHARGE DEVICES I Filed June 7, 1945 [/v TURZ'EUGENE LEM/WERE.

H/s ATTUPNEY Patented Get. 21, 1947 CIRCUIT FOR ELECTRIC DISCHARGEDEVICES Eugene Lemmers, Cleveland Heights, Ohio, assignor to GeneralElectric Company, a corporation of New York Application June 7, 1945,Serial No. 598,121

4 Claims.

This invention relates to circuits for electric discharge devices, andespecially to resonant starting circuits. The invention is useful forfluorescent lamps of the usual low pressure positive column type, aswell as for other discharge lamps. Important objects of the inventionare to provide higher voltage for starting the discharge than insubsequent operation, and to assure proper preheat of the dischargeelectrodes or cathodes before starting. The invention also aims to avoidhigh current surges that might injure lamps at starting, as well assubstantial power losses during operation. The invention obviates theliability to premature starting of a discharge between cold orinsufficiently heated cathodes, owing to erratic high voltage transientsacross resonant circuits at the instant of switching on, which largelydepend on the point of the A. C. voltage cycle where switching onoccurs. Other features and advantages of the invention will appear fromthe description of species and forms of embodiment, and from thedrawings.

In the drawings, Figs. 1 and 2 are diagrammatic illustrations ofdischarge lamps with lead and lag circuits embodying the invention insimple forms, and Figs. 3 and 4 illustrate modifications of the startingcircuit.

Figs. 1 and 2 each show a low pressure positive column discharge lamp lconsisting of an envelope tube equipped with widely spaced cooperatingelectrodes 2, 2 in its opposite ends. Either or each of the electrodes2, 2 may be a thermionic activated cathode embodying an electric heaterfor bringing it to a temperature of electron emission before thedischarge between the electrodes is initiated. For instance, theelectrodes 2, 2 may consist of tungsten filament wires, in coil orcoiled coil form, charged or coated with activating alkaline earthoxides, such as a mixture including barium and strontium oxides. Theenvelope I may contain an atmosphere of gas or vapor or both at lowpressure: e. g., an inert rare starting gas, like argon at 2 to 6 mm. ofmercury, and a supply of mercury that is indicated by a droplet 3. Also,an internal coating of luminescent material or phosphor 4 excitable bythe radiation from the discharge is indicated on the envelope wall.

As shown, the electrodes 2, 2 are connected to opposite sides of adischarge circuit which may be energized from any suitable A. C. source,such as a 110 volt cycle lighting circuit (not shown), and may includethe usual inductive ballast 6, as well as a control switch I. A startingcircuit 8 is shown connected across the discharge circuit 5 in parallelwith the discharge device I, between and through the cathode resistances2, 2. In the case of'a lead circuit, Fig. 1, a capacitor or condenser 9may be included in one side of the discharge circuit in series with thedischarge device; or in the case of a lag circuit, Fig. 2, in thestarting circuit 8 that is in parallel with the discharge device I.

In accordance with my invention, I include in the starting circuit 8 aninductance l0 and a resistance device or resistor l l, in series withone another. The value of the inductance 6 (and that of the capacitor 9,when in circuit 5) are so chosen that during operation the desireddischarge current and a voltage less than the supply voltage on thecircuit 5 are maintained across the electrode gap 2, 2 of the dischargedevice I. The value of the inductance l0 (and that of the capacitor 9when in the circuit 8) is then chosen so that with a low or zeroresistance value for resistor II, the circuit 5 with its inductance 6and the circuit 8 with its inductance l0 together constitute a resonantcircuit in which the voltage across the electrode gap 2, 2 exceeds thesupply voltage on the circuit 5 and the break-down voltage of the lamp IWhen cold (or at ordinary room temperature of some 20 C'.), the resistorII has a resistance so high that the combined circuit 5, 8 shows verylittle resonance; but this resistor II has a fairly large negativetemperature resistance coefficient, and is so proportioned as to beheated by the current through it to a temperature at which itsresistance becomes inconsiderable during a length of time not less thanthat required for the current to heat up the oathodes to a temperatureof adequate electron emission, or perhaps slightly exceeding this.Resistors of these characteristics are commercially available, and maybe of the type comprising carborundum or silicon carbide. Of course aresistance device of like characteristics but heated by a separateresistance or other heater might be used.

When the circuits 5, 8 are first energized by closing the control switchI, the circuit resistance 3 due to resistor I l is so high that verylittle effective resonance exists in the combined circuit. By virtue ofthe high resistance of resistance II at this time and the consequent lowcurrent which flows in the starting circuit 8, the inductive re- 5actance of inductance I0 is high so that the combined reactances ofinductances 6 and ill is substantially greater than the capacitivereactance of capacitance 9. As the resistor ll heats up and itsresistance decreases, the current in the com- 10 bined circuit 5, 8increases, and likewise the Q of this circuit 5, 8 inasmuch as theincreased current flowing in the circuit reduces the inductive reactanceof inductance l0 until there is enough resonance to give a Voltageexceeding the break-- down voltage of the lamp I, whereupon thedischarge starts and becomes established in the lamp. The discharge onceestablished, the effective impedance of the lamp l becomes less thanthat of the circuit 8, and the resistor I I cools ofi, resulting in aprogressive, cumulative increase of the circuit 8 impedance andresistance, and in reduction of the current in this circuit. Thisviretual removal of the inductance l0 from across the lamp l increases theefficiency of the circuit as a whole.

For the convenience of those i'wishing to use -my invention, I"will now.give illustrative values of circuit constants suitable for an ordinarycommercial 15 Watt positive column fluorescent lamp 1 of usual 18' inchtube length and 1 inch diam- .eter; but these-are not to be understoodas definingbr limiting tl'ie'invention in its broader aspects.

.In the case of the lead circuit of Fig. 1, the in- '3 ductances fi and'lfl mayeach be wound to give 'a 160 voltdrop on a '60 cycle -A.Cficurrent of 0.330 amp. R. M. S., with a D50. resistance of 20 ohms orless; the capacitor 9 maybe*a3 microfa'rad condenser;'the resistance llmay have a cold nc-current value of 200'ohms at room In the case ofthelag'c'ircuitof Fig. 2, the values of the circuit constants maybe thesame except 5 for the inductance 6,'which' may be wound to give alOOvolt drop on a 60 cycle A. C. current of 0.330

"Fig. 3"illustrates the adaptation' ofthe*Fig. 1

lamps I, I connected in series across the discharge circuit 5, andea'chshuntedwith a starting circuit-8 or 8'-'includin g an inductance ill orID.

As shown, only-oneof the starting circuits B,- 8

includes a resistor l l.

circuits to a'plu'rality of discharge devices or' Fig.4 illustratesanother adaptation of theFig.

-1 circuits to a plurality 5 of discharge *devices or lam'ps l, Iconnected in series across the discharge circuit 5. Here a's'inglestarting circuit with one another shunts the serially connected lamps I,I, Provision for flow of current to preheatthejadjacent'cathodes 2, 2 ofthe lamps l, l

is made by connecting these cathodes into a heatto the startingcircuit'Bbymeans of a coil [3 which coacts as secondary with the coil of theinductance ID as primary, andmay be wound on' the same core.

'B incIuding inductance 'Ifland resistor II in series ing circuitloop.l2 'which is inductively coupled In Figs. 2,'3,"and'4, variousparts and features are marked with the same reference numerals as thosecorresponding in Fig. 1, as a means of dispensing with repetitivedescription-a distinctive prime being added where such distinction seemsdesirable.

What I claim as new and desire to secure by Letters Patent of the UnitedStates is:

1. The combination with an alternating current supply circuit, anelectric discharge circuit embodying inductive ballast, an electricdischarge device employing an ionizable medium and having eletrodesconnected across sai'd' 'discharge circuit,-at least one ofsaid='electrodes--being thermionic and embodying electric heating meansconnected to the corresponding side of said dischargecircuit, and astarting circuit connected 5 across said discharge circuit through saidheating means, of an indutance and a current-heated electric resistancedevice of negative temperature resistance coefiicient serially connectedin said starting circuit; and capacitance also included in the combineddischarge and starting circuit, whereby the same is rendered resonantafter said device heats up.

2. Ihe combination with an alternating current supply circuit, anelectric discharge circuit embodying inductive ballast, an electricdischarge device employing an ionizable medium and having thermionicactivated refractory wire coils circuit correlated with said inductiveballast to form a resonant circuit afiording a discharge initiatingvoltage across the discharge device when the discharge circuit isenergized, and a serially connected electric resistance in said startingcircuit having when cold arelatively high value, suific'i'ent tosubstantially nullify the combined circuit resonance, and having suchheat capacity and such a negative temperature resistance coefificient asto heat up and substantially lose its resistance by the time.currentfiow through said coils brings them to emissive temperature,whereby the resonance-becomes effective to initiate discharge.

3. In combination, an alternating current supply circuit, an electricdischargedevice-Of the type employing an ionizable medium-and having atleast one" electrode of the filamentary type, a discharge circuitconnected between electrodes of 'saiddischarge device and said supplycircuit and including an inductive ballast,'a starting circuit connectedacrossele'c'trodes of said device and comprising-aninductance and aserially connected resistance having-a negative temperature resistancecoefiicient, and a capacitance connected in circuit with said dischargecircuit and said start- -ting circuit, the value of said resistance atstart- -ing being-such that the inductive reactance of saidinductancerenders the combined starting and discharge circuitnon-resonant and the subrelatively high voltage is impressed across saidelectrodes to initiate an arc discharge in said .device after theelectrode has assumed a safe operating temperature.

4. In combination, an alternating current supply circuit, an electricdischarge device of the type employing an ionizable medium and having atleast one electrode of the filamentary type, a discharge circuitconnected between electrodes of said discharge device and said supplycircuit and including an inductive ballast, a starting circuit connectedacross electrodes of said device and comprising an inductance and aserially connected resistance having a negative temperature resistancecoefficient, and a capacitance connected in series with said dischargeand said starting circuits, said resistance controlling said inductanceupon the flow of current therethrough to render said starting anddischarge circuits resonant so that a relatively high voltage isimpressed across said electrodes to initiate an are discharge in saiddevice after the electrode has assumed a safe operating temperature.

EUGENE LEMME'RS.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS 10 Number Name Date 2,170,447 Edwards (a) Aug. 22,1939 2,170,448 Edwards (b) Aug. 22, 1939 2,284,407 Edwards (0) May 26,1942 2,231,999 Gustin Feb. 18, 1941 15 2,351,499 Freeman June 13, 1944

